I hate this too! I wish they'd code something in that makes the villagers stay still when you have the camera app open. It's almost impossible to get a decent photo with them as it is.
I agree. I wouldn't even mind if they decided that the animals would only do that if your friendship level with them is high. And, to carry the idea a little further, maybe when the friendship level is at its highest, the villager would make a pose that is unique to their personality type or hobby type.
I've had this happen before. This also reminds me of the issue of trying to gift them something, but they are sitting on a bench and just refuses to stand up! Really do wish you could gift them while they're sitting down. Doesn't make too much sense why you can't.